The TV chef's latest venture is a second high street restaurant chain with a new concept which is being kept secret

Jamie Oliver is cooking up another assault on the high street with plans for a chain of restaurants called Union Jack’s.

Oliver is understood to be encouraged by the success of Jamie’s Italian, which opened three years ago. It now has 18 branches, with another five to open in the next few months. Sales were £19m in 2009, according to the most recent publicly available accounts.

Work on the latest venture is in the early stages and details of the new concept are being kept under wraps. It is not even clear what type of cuisine the restaurants will offer.

A spokesman for Oliver declined to comment beyond confirming that the chef had plans for a second chain. He said: “We are working on a new restaurant concept called Union Jack’s but we are at an early stage with this and the exact type of food on offer hasn’t been